1. Field of the Invention
The present invention relates to an intercrystalline semiconductive ceramic capacitor having an intercrystalline insulation layer among semiconductive crystal grains of a multicrystalline structure mainly consisting of SrTiO.sub.3, and more particularly to an intercrystalline semiconductive ceramic capacitor made by sintering a composition containing TiO.sub.2, Dy.sub.2 O.sub.3, ZnO, MnO.sub.2 and Al.sub.2 O.sub.3 in a small amount as its minor component in a reducing atmosphere to achieve a tightness of microstructure and a promotion of a crystal growth, thereby exhibiting a superior electrical characteristic.
2. Description of the Prior Art
Intercrystalline semiconductive ceramic capacitors containing BaTiO.sub.3 or SrTiO.sub.3 as a major component have, as a dielectric layer, a thin intercrystalline insulation layer formed among semiconductive crystal grains. By this layer, such ceramic capacitors exhibit a high apparent dielectric constant, as compared with general ceramic capacitors. This high apparent dielectric constant provides advantages of a compactness and a high capacity.
Among intercrystalline semiconductive ceramic capacitors, SrTiO.sub.3 -based ceramic capacitors are known as exhibiting a low dielectric loss (tan .delta.) and a superior temperature dependency of dielectric constant at a room temperature over BaTiO.sub.3 -based ceramic capacitors, because they contain SFTiO.sub.3 as a major component.
As a composition for such SrTiO.sub.3 -based ceramic capacitors, there has been known a composition essentially consisting of SrTiO.sub.3 added with Nb.sub.2 O.sub.5 and SiO.sub.2 in a small amount. The SrTiO.sub.3 -based ceramic capacitors can be manufactured by sintering the dielectric ceramic in a reducing atmosphere, diffusing an insulation material comprised of a metal oxide such as PbO, Bi.sub.2 O.sub.3, B.sub.2 O.sub.3 or CuO in crystal grain boundaries of the semiconductive ceramic and thereby forming an intercrystalline insulation layer.
However, this conventional intercrystalline semiconductive ceramic composition exhibits a dielectric constant of about 40,000. As a result, intercrystalline semiconductive ceramic capacitors made of such a composition has a limited capacitance per area. By such a limited capacitance, the ceramic capacitors can not achieve a compactness.